The present invention relates to radio communication systems, and more particularly to radio systems deploying different air interfaces for short-range/high-rate communications, and long-range/low-rate communications.
In recent decades, progress in radio and Very Large Scale Integrated circuit (VLSI) technology has fostered widespread use of radio communications in consumer applications. Portable devices, such as mobile radios, can now be produced having acceptable cost, size and power consumption. Although wireless technology is today focused mainly on voice communications (e.g., with respect to handheld radios), this field will likely expand in the near future to provide greater information flow to and from other types of nomadic devices and fixed devices. More specifically, it is likely that further advances in technology will provide very inexpensive radio equipment which can be easily integrated into many devices. This will reduce the number of cables currently used. For instance, radio communication can eliminate or reduce the number of cables used to connect master devices with their respective peripherals. The aforementioned radio communications will require an unlicenced band with sufficient capacity to allow for high data rate transmissions. A suitable band is the Industrial, Scientific and Medical (ISM) band at 2.4 GHz, which is globally available. The band provides 83.5 MHZ of radio spectrum.
To allow different radio networks to share the same radio medium without coordination, signal spreading is usually applied. In fact, the Federal Communications Commission (FCC) in the United States currently requires radio equipment operating in the 2.4 GHz band to apply some form of spreading when the transmit power exceeds about 0 dBm. Spreading can either be at the symbol level by applying direct-sequence (DS) spread spectrum techniques, or at the channel level by applying Frequency Hopping (FH) spread spectrum techniques. The latter is attractive for the radio applications mentioned above because it more readily allows the use of cost-effective radios. A system called BLUETOOTH(trademark) has recently been introduced to provide pervasive connectivity, especially between portable devices like mobile phones, laptop computers, Personal Digital Assistants (PDAs), and other nomadic devices. This system applies frequency hopping to enable the construction of low-power, low-cost radios with a small footprint. The system supports both data and voice. The latter is optimized by applying a robust voice coding in combination with fast frequency hopping with a nominal rate of 1600 hops/s through the entire 2.4 GHz ISM band. The system concept includes piconets consisting of a master device and a limited number of slave devices sharing the same 1 MHz channel. With its maximum output power of 20 dBm, it covers areas with radii up to about 100-200 m. Over this extended range, a maximal data rate of 1 Mb/s can be supported.
When the BLUETOOTH(trademark) system operates with output powers above 0 dBm, power control becomes mandatory. This power control is based on a closed-loop control as is described in U.S. patent application Ser. No. 09/156,695 entitled xe2x80x9cAutomatic Power Control in Uncoordinated FH Radio Systems,xe2x80x9d filed Sep. 18, 1998 which is hereby incorporated herein by reference in its entirety. At the receiver, the signal strength is measured. The transmitter is then requested to increase or decrease the transmitter power level so that the received power level falls within a certain power window. Power control based on received signal strength indication compensates for path loss, not for interference. This type of power control is preferred in uncoordinated ad-hoc systems because it reduces mutual interference.
For applications demanding higher data rates, the system can be extended with a high-speed mode. A description of a possible air interface for this high-speed mode is presented in U.S. patent application Ser. No. 09/385,024 entitled xe2x80x9cResource management in uncoordinated FH systems,xe2x80x9d filed Aug. 30, 1999 which is hereby incorporated herein by reference in its entirety. Since increasing the bit rate has the effect of reducing the energy per bit, either the power has to increase, or the range must be decreased. Increasing the power is limited by radio implementation, current consumption, and also by governmental regulations. The FCC allows high-power radios to operate with transmit powers exceeding 0.75 mW in the 2.4 GHz band, but in these cases requires the radios to apply spread spectrum techniques. DS spreaders are not cost or power efficient, nor is implementation trivial at high bit rates because the necessary chip rates increase tremendously. FH spreaders are limited to rates of 1-2 Mb/s because of the bandwidth restriction of 1 MHz. Therefore, only those high-rate modes operating at low power (i.e., below 0.75 mW) are considered, because at low power, the use of spreading techniques is not required. The use of low power, however, puts restrictions on the range. This means that two dual-mode radios that want to switch from the low-speed mode to the high-speed mode have to be sufficiently close to one another. Yet, because the low-rate connection covers larger ranges and is used for connection establishment, for two units that connect at the low-rate, it is unclear whether a high-speed connection can be supported between them as well.
There is therefore a need for methods and apparatuses that enable a dual-mode radio to assess whether a high-speed connection is feasible.
It should be emphasized that the terms xe2x80x9ccomprisesxe2x80x9d and xe2x80x9ccomprisingxe2x80x9d, when used in this specification, are taken to specify the presence of stated features, integers, steps or components; but the use of these terms does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
In accordance with one aspect of the present invention, the foregoing and other objects are achieved in methods and apparatuses that determine whether a first kind of communication link can be supported between a first unit and a second unit, wherein the first kind of communication link does not support a transmission range above a first maximum value. This is accomplished by using a second kind of communication link to determine a propagation loss value between the first unit and the second unit, wherein the second kind of communication link supports the transmission range above the first maximum value. Then, the propagation loss value is used to determine whether the first kind of communication link can be supported between the first unit and the second unit. As examples, the first kind of communication link may be a high speed link, and the second kind of communication link may be a low speed link.
In another aspect, using the propagation loss value to determine whether the first kind of communication link can be supported between the first unit and the second unit can comprise using the propagation loss value and a maximum transmission power level associated with the first maximum value to estimate a received signal strength value. It is then determined that the first kind of communication link cannot be supported between the first unit and the second unit if the estimated received signal strength value is below a predetermined value. Otherwise, it is determined that the first kind of communication link can be supported between the first unit and the second unit if the estimated received signal strength value is not below the predetermined value.
In some applications of the invention, the first kind of communication link may be one that does not include use of spread spectrum techniques, and the second kind of communication link may be one that does include use of a spread spectrum technique.
In another aspect of the invention, using the second kind of communication link to determine the propagation loss value between the first unit and the second unit can comprise, in the first unit, measuring a received signal strength value of a signal transmitted by the second unit. The propagation loss value between the first unit and the second unit is then determined as a function of the measured received signal strength value and a transmission power level used by the second unit.
In some embodiments, the first unit may be a master unit and the second unit may be a slave unit. The master unit and the slave unit may communicate in accordance with BLUETOOTH(trademark) standards.
In other embodiments, the first unit is a first slave unit in a piconet, and the second unit is a second slave unit in the piconet. The signal transmitted by the second unit in these cases is transmitted to a master unit in the piconet. In such embodiments, the step of, in the first unit, measuring the received signal strength value of the signal transmitted by the second unit can comprise, in the first unit, receiving a first packet transmitted by the master unit; and determining whether a packet address included in the first packet identifies the second slave unit. Then, the received signal strength value of a second packet transmitted in a next time slot is conditionally measured if the packet address included in the first packet identifies the second slave unit.
The piconet may operate in accordance with BLUETOOTH(trademark) standards.